Electronic indicator system for radar with spinning antenna or the like



March 14, 1950 N. E. LlNDENBLAD ELECTRONIC INDICATOR SYSTEM FOR RADAR WITH SPINNING ANTENNA 0R THE LIKE 2 Sheets-Sheet 1 Filed Aug. 13, 1942 wmf-lll.

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March 14, 1950 N. E. LINDENBLAD 2,500,552

ELECTRONIC INDICATOR SYSTEM EoR RADAR WITH SPINNING ANTENNA 0R THE LIKE Filed Aug. 13, 1942 2 sheets-Sheet 2 ATTORNEY Patented Mar. 14, 1950 ELECTRONIC INDICATOR SYSTEM FOR RADAR WITH SPINNING ANTENNA OR THE LIKE Nils E. Lindenblad, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application August 13, 1942, Serial No. 454,661 /f-J 10 Claims.

This invention relates in general to a method of and apparatus for indicating on an oscilloscope a particular beam position of an antenna which assumes a plurality of different positions periodically.

In obstacle detection systems, sometimes known as radio locators, it is now proposed to cause a small deflection of a radio beam at regular intervals through the four quadrants of a circle which is perpendicularly located to the mean axis of the beam. This can be done either by wiggling the whole antenna system. or (for example, in the case of an antenna utilizing a parabolic reflector with a radiating element positioned slightly oifcentene'ccentrically, so to speak) by spinning the radiating element in a. circle, or by spinning a deflecting element olf the focus of the reflector. ,Such an antenna system, when employed for radio locating purposes, must not only be able to produce the beam deflections at regular intervals, but must be freely movable in all directions for scanning purposes and for pointing the antenna directly on the object to be detected.

The present invention provides, among other things, a simple and efficient method of indicatingon an oscilloscope a mark characteristic of a particular beam position of the antenna system. The invention utilizes a minimum of auxiliary circuits, a minimum of control conductors, and successfully avoids the consequence of the ran- `dom choice of synchronous position between the antenna beam deecting device and the indicator prime mover.

The following is a detailed description of the invention accompanied by a drawing, wherein Fig. 1 illustrates the invention used in connection with a pulse type radio locating system, Fig. 2 is a circuit detail which can replace a mechanical switch shown in Fig. l, Figures 3 and 4 are views showing for two different conditions the appearance of the image obtained on the screen of the cathode ray tube employed for indicating antenna beam position with respect to target in the horizontal plane, and Figures 5 and 6 are views showing for two different conditions the appearance of the image obtained on the screen of the cathode ray tube employed for indicating antenna beam position with respect to target in the vertical plane.

Before proceeding with a description of the invention, it is believed helpful to refer to the type of radio locating system which is shown employed in Fig. 1. The radio locating system is generally of the type described in my copendlng application Serial No. 441,311, filed May l,

1942, now Patent No. 2,411,140 issued November 12, 1946, which employs a transmitter for transmitting periodically repeated radio wave pulses of extremely short duration. A receiver is used to receive the pulses which are refiected by the object to be detected. This system employs a directive antenna and other expedients at both transmitter and receiver by means of which the indications are confined to objects lying within a narrow range of angles. In order to produce the radio wave pulses, the oscillator of the transmltter is excited periodically through a spark gap switching device which is in series with the oscillator and the charging voltage source and to which is supplied at periodic intervals a voltage of sufficient value to break down the gap.

The transmitting antenna of the pulse type radio locating systems described above preferably comprises a parabolic antenna having, off-center, an eccentrically positioned radiating element which is rotated by a two-pole synchronous motor at about sixty times per second. The entire system is designed to radiate a pulse of ultra high frequency energy in each of the four quadrants of the circle traveled by the radiating element in each revolution. At a speed of rotation of sixty times per second, the pulses will be radiated 240 times per second, corresponding to a pulse for each quadrant position of each revolution of the antenna. The up and down beam ring positions of the radiating element determine the vvertical position of the object to be detected,

lap in the right and left beam ring positions.

Since the time interval between radiated pulses is quite long compared to the time of each pulse, it will be understood that a pulse reflected by a remote object tobe detected will be received at the receiver located adjacent the transmitter during the same quadrant of rotation in which the original pulse is radiated.

If the pulses which are reflected from a remote object were originally radiated in the up and down positions of the rotating radiating element, these pulses will be received during the same up and down positions, and if these received pulses are of equal intensity, it follows that the horizontal plane of antenna system is pointed at the 3 object. If the reflected pulses received during the right and left positions of the rotating radiatingr element are also of equal intensity, it follows that the vertical plane of the antenna system is also pointed at the object. Under these conditions, the object to be detected is in a direct line with the focus of the antenna. If now, the parabolic reflector of the antenna is made of widely spaced wires in mesh formation, and the object is within visual distance, the illumination of a searchlight placed directly behind the reflector will illuminate the object.

If the received pulses reflected from the object are of unequal intensity, it is an indication that the antenna system is not pointed directly at the object, but to one side of the object.

The reilected pulses which are received are viewed on a pair of cathode ray Oscilloscopes, one of which indicates the pulses received during the up and down positions of the rotating radiating element, and the other of which indicates the pulses received during the right and left positions of the rotating radiating element.

inasmuch as a two pole synchronous motor is employed to rotate the antenna system, and since this motor can start either in the up or down position of the radiating element, it is important to provide a determination of Whether the first reflected pulse received back from the object to be detected corresponds to either the up or the down position. The present invention furnishes a simple and enicient method of and apparatus for making this determination.

Referring to Fig. 1 in more detail, there is shown a pulse transmitter comprising an ultra high frequency oscillator M (here shown by way of example as a magnetron) capable of producin oscillations of about ten centimeters wavelength. This oscillator is periodically charged with a high polarizing potential through a spark gap T (air blast type) in circuit with a line TL. The end of line TL which is furthest removed from the spark gap T is connected through a rectifier L to the secondary winding of an induction coil P whose primary winding is connected to a main charging system comprising a souree'of direct current N and a switching device U. This part of the system serves to convert a relatively low voltage direct current charging potential from N to periodic high voltage pulses for charging line TL and corresponds to Figure 4 of my Patent 2,411,140. Reference is here made to my United States Patent 2,275,635, showing pulse charging circuits of interest in this connection.

A trigger spark system comprising an induction coil G, an auxiliary spark gap electrode associated with spark gap T, and a switching device F insures sparking at gap T only when line TL is fully charged and between charging pulses supplied to line TL by system U. That is, the trigger spark system insures the discharge of line TL across gap T and into the magnetron M between the times that the rectifier L is passing charging pulses to the line TL. The trigger spark switch device F is like the switching device U in that when one brush is connected to a segment on the commutator, the other brush of the same switching device is on an insulating segment or portionvof the same commutator, and vice versa.

The directive antenna for radiating the extremely short pulses of ultra short wave carrier energy is indicated at A and comprises a rotatable radiating element positioned off the center of a parabolic reflector. This radiating element is driven by a two-pole synchronous motor appropriately labeled. at a speed of 3,600 R. P. M., corresponding to sixty revolutions per second. The system is so designed that during each quadrant of the circle of each revolution of the radiating clement, the magnetron will deliver a pulse tu the antenna over connections X and Y, as a result of which there will be 240 pulses radiated per second. Each pulse may be of the order of one microsecond duration, or so.

Linked to the same shaft of the two-pole synchronous motor which drives the rotating radiating element, is a rotating arm I0 which makes contact with an arcuate metallic segment of switch SD for a time slightly greater than the duration of one quadrant. The arcuate shaped segment is of such length that arm IIJ will engage it during the time the radiating element is, by Way of example, in the up position and also in the right position at right angles to the rst mentioned position. Associated with arm I0 is a bias battery I I for supplying through the arcuate segment a bias to certain plates of the cathode ray Oscilloscopes K1 and K2 for changing the origin of the cathode ray spot on the oscilloscopes. This will be described in more detail later.

The receiver 50 which receives the pulse reected from the object to be detected, is connected to the radiating element of antenna system A through lead I2, concentric line resonator D, and line Z. Line Z is an odd multiple of a. quarter wave long for energy of the carrier frequently generated by magnetron M.

Lead Y is coupled to the magnetron oscillator at C by means of a small loop, and is connected to the junction point B of leads Y and Z. This lead Z is an odd multiple of a quarter wave and is matched from an impedance standpoint to lead Y extending to the antenna, for pulses outgoing from the magnetron.

When short wave carrier pulses are sent out by the magnetron over lead X, the resonator D is energized through lead Z and this causes the spark gap E in the interior of the resonator to break down, thus producing a detuning action in D, as a result of which lead Z becomes a high impedance when looked at from point B. Thus, the main portion of the energy obtained from the magnetron M travels out to the antenna to be radiated thereby, and only a small portion of the energy derived from the oscillator passes over lead Z to maintain the spark across the gap E in resonator D.

As for energy received by the antenna A, the lead X is not matched at point C since it is closed at this point. Because the lead X has an electrical length equal to an odd multiple'of a quarter wave length, the impedance of lead X at point B as seen from the antenna is high. However, energy received on the antenna will energize resonator D without producing sparking at E, as a result of which the radio frequency energy in resonator D will pass to the receiver 50 for subsequent utilization by the Oscilloscopes K1 and K2. The reason why the incoming or received energy will not cause the spark gap E in the resonator to break down while the outgoing energy from the magnetron M will cause a breakdown of the gap E, is because the latter energy is far more intense than the former.

When the magnetron is caused to oscillate by virtue of the surge of current through the spark gap T, the current through the magnetron will it or reactance asf` ajresultofz-which-a pulse is initiated'whichis' -through p ulse ampliiler Va. whose oui:-l

. Dllt'v-, ausesthe saw'tooth generator Wto start.

This sawltothfgenerator-workson the rst grids 4 naher-,v1 '-vl, thus controlling the currentthro'ugh-the tubes. The time? constants v otthe'saw toothfgeneratorareadius'ted lfor.. the4 distance range to be' observed, by making the time of sweep of the generator correspond toth'e distance tcsbechecked AS .mi

duced by resistors I3 and M, respectively, and

`willpass currentV when the cathode bias is reduced. The reduction in cathode bias to render the'` tubes V11 and-V: conductive is obtained by means of switch S. The. contact arm of switch Sis connectedl to ground and rotates to cause.

engagement with segments Ni to N4 and Oi to O4. `Segments N1 'to N4, inclusive, are connected to.- gether and to a pointl on cathode bias resistorv 14.

vSeg'mentsvOr` to 01,' inclusive, are also connected together and to a point on cathode biasresistor Il. It'y should be noted that the segments' labeled. N1,v N2, Nsand N4 alternate with the segments labeled O1, O2, O: and O4. The rotating switch or 'scope selector S may be driven by a synchronous motor having any number of poles.

I f, as shown in the drawing, a four-pole machine A is ch'osen, the number of segments on the selector commutator vwill bey eight. Alternatev conc tacts or segments-of. the selector S are connected together, and each such group of four contacts controls the on -and` oil condition for the sawtooth sweep of each of the two cathode ray os- 4cilloscopes Kr and K2. Oscilloscope Krwill give a horizontal sweep, while oscilloscope K2 will give a vertical sweepfin the particular arrangement illustrated.

' When'vacuum tubes V1 or V2 pass current, the

voltage drop fin resistors Q1 or Q2, respectively, 1'

,in the up'position and in the rightfposition ofthe rotating. radiatingI element,v will cause the sweep starting points on the Oscilloscopes tobe .slightly displaced relai'dveV to the sweep starting points when theradiating element i's vin the down position and in the left position.

In the operation of the system'as a whole, let us 'assume that the switch SD is in the position shown in the drawing. 'Ihe spark gap T will break down in the quadrant in which the switch SD is shown (gap T breaks down once in eachl quadrant in each revolution of the radiating element), as a result of which a pulse fromv the magnetron will pass out tothe radiating element. This same pulse will produce a high impedance at point B looking toward the receiver aportionof the p'ulse from the magnetron will pass; through ampliiler' Va which will cause the startof the saw-tooth generator W. TubeV2 will be conductivebccause of the decrease in its cath- 'ode bias, assuming the switch S to' be at this particular momenton one generator through tube 4V2 will nowproduce a vertical sweep of the cathode ray in oscilloscope nectedf-toxthe lower vertical v deection plate ot oscilloscope K2, while the anode of tube V1 isconnected to the left'horizontal deiiection plate of oscilloscope K1. This vertical sweep is scaled according to the range of distances to be observed from the antenna to the object to be detected.

A reected ywave (sometimes called an echo) returned from the object to be detected will pass' through the receiver l0 and cause a horizontal deilection on oscilloscope K2 by means oi the right ha'nd deflection plate of K2 in circuit with the video output of the receiver. (It should be understood that the receiver is now in condition to receive because the outgoing pulse which blocks the receiver extremely short compared to the time intervalbetween successive outgoing pulses.) This horizontal deilection willk be some distance down on the vertical sweep of &,.dependin'g on the time for the original transmittedfpulse to be returned as an echo or reilected pulse to the antenna." The extent of Vhorizontal deviation ofthe sweep is a measure of the intensity of the returned (reflected) pulse. in scope. K2 will continue during the horizontal deflection producedv .by the returned pulse and gives width to the observed pulse.

The bias on arm I 0 of switch SD Vis connected across'the grounding resistor R1, by .virtue of connection l5. Thus, resistor R1 is 1in circuit with one vertical plate of oscilloscope K2 and .particular up position corresponding to the quadrant vat which thebias is effective. Horizontally` observed deiiections on the vertical' sweep oscilloscope K2 caused by reected pulses received during the time the antenna is in the up position will thus be displaced vertically from the deections on the same oscilloscope K2 caused by the reflected pulses received during the time the antenna. is in the down position.

Inasmuch as the arcuate segment of switch SD isslightly longer than 90, itis'eifective for the up vertical position of the antenna and also for the right horizontal position of the antenna.v Consequently, echo or reected pulses passed on by the receiver 50 to the oscilloscope K1 while the antenna is in the right and left horizontal positions will produce vertical deilections on the horizontal sweepof the oscilloscope K1, but the bias on arm I0 of switch SD will change the location ofthe origin of the ray spot (sweep starting point) in K1, so that the operator can determine when the antenna is in the particular right horizontal position.

The horizontal deilections on the vertical sweep oscilloscope K2 due to received pulses passed on during the up and down positions of the antenna will appear one above the other, and similarly,-

the vertical deections on the horizontal sweep oscilloscope K1 due to received pulses passed on rotating contact of I The vertical sweep will appear adjacent each other.' Due vtti-,thev

speed of rotation of the antenna through its four quadrants and the rapidity of the radiated pulses,

the deections appearing on the Oscilloscopes will appear stationary on account of the of vision.

Figures 3 to 6 show the appearance of the horizontal and vertical deflections or pips on the screens of the tubes K2 and K1, respectively, for different positions -of the antenna beam center axis with respect to the target as indicated by the legends.

An advantage of the present invention lies in the fact that the operator can always determine immediately which deflections on the oscilloscopes correspond to the different positions of the spinning antenna, despite the fact that the synchronous two-pole motor driving the antenna can lock in synchronism at either of two positions displaced 180 with respect to each other.

Fig. 2 illustrates a quarterphase network system which can replace the oscilloscope selector switch S. This system includes a network having two branches arranged in electrically parallel relation and connected between ground and a source of sixty cycle supply. One branch includes a condenser 2| and two resistors R2, R3 in series, while the other branch includes an inductance coil 22 and a resistor R4 in series. A pair of connections 23 andv 24 extend from suitable points on the network branches to the primary windings of audio `transformers 25 and 26, respectively, whose secondary windings are connected to rectifiers 2l, 28 and 29, 30 for producing pulses which can be applied to the second grids of the tetrode vacuum tubes Vi and V2 of Fig. 1. Due to the fact that the voltages in the two branches are 90 out of phase relative to each other, the pulses from the rectiers Will supply pulses alternately to the grids of the vacuum tubes V1 and V2 to render these tubes alternately conductive.

What is claimed is:

1. A directive antenna system comprising al -parabolic reflector and a radiating element positioned off-center in front of said reflector, a motor driving said element in a circle about the axis of said reflector, a pair of cathode ray tubes one for indicating the vertical positions of said radiating element, and the other for indicating a the horizontal positions of said radiating element, translating apparatus coupled between said radiating element and said cathode ray tubes, and circuit means coupled to said cathode ray tubes and supplying a bias to said tubes in only one vertical' position and in only one horizontal position of said radiating element for producing indications characteristic of` these positions of said radiating element.

2. An obstacle detection system comprising a transmitter for periodically sending short Wave persistence,v

' chronous driving motor for causing said antennal j to assume sequentiallyfour different beam firing' positions corresponding tothe fourquadrantsol? 'a circle, first andf'se'cond cathode ray tubesf each j' o f said small arc is identiable.

having' electron lray deflection elements,I transv lating apparatus coupled betweenrsaiddirective; f- 'antenna and said l` :a'.thode v-raytubi'es', an arcuate", 'l shaped segment overlapping.two adjacent "quad-f rants of the circular path travelled*byl said'anll tenne and adapted. to 'bgenergizedeurmg the', i time said antenna is passing'gythrougn said'ft'zwo4 i i quadrants, and a circuitlconnection from Asaid segment to different electron ra'y'-v de'ectionelements of said cathode tubes, whereby said tubesA provide indications characteristicof the positions of said antenna in all four quadrants. 'Y 4. An antenna adapted to sequentially assume different beam positions, a motor linked to said antenna through a drive shaft, means drivenvby said drive shaft and arranged to close an electrical circuit during only a relatively small arc of the circle traversed by said shaft while itis rotating, a cathode ray oscilloscope having elec-y tron ray deflecting elements, a sweep circuit connected to certain of said deecting elements, said,V electrical circuit includingvmeans for applying a potential of predetermined duration to another of said dcflecting elements of said'cathode ray oscilloscope, whereby the particular beam position of said antenna corresponding to the position 5. An object detection system including a directive antenna comprising a reector and a radiatr ing element eccentrically positioned in front oi',y said reector, a motor having a shaft linked to'` said element for rotating the same, and means" for transmitting a single pulse of ultra short wave energy to said element for each quadrant of the circle through which said element yis rotated, said pulses being uniformly spaced and being short compared to the time intervals between them, a receiver coupled to said antenna, and f means in said system for distinguishing betweenthe pulses received during the different quad-v rants.

6. An object detection system including a directive antenna, a motor for effectively causing the antenna to assume different positions Vof eifectiveness in a circular path, means for transmitting a single pulse of high frequency energy, from said antenna during each quadrant of said circular path, said pulses being uniformly spaced and being short compared to the time intervals'.vv

between them, a receiver coupled to said antenna, and means in said system for distinguishingbef tween the pulses received during the differentv quadrants.

carrier pulses of short duration spaced in time v an amount which is large compared to the time of each pulse, a directive antenna system for said transmitter including a parabolic reflector having a radiating element positioned off-center, a two-pole synchronous motor for rotating said radiating element in a circular path, whereby said antenna system periodically assumes a plurality of beam positions, an electronic tube system, and means coupled to said rotating radiating element for app-lying to said electronic tube system potentials during only such times when said radiating element isin certain positions.

'3. A directive antenna having a two-pole syn- 7. For use with a radio locating system which transmits a single pulse from-a rotating antenna; structure during each of the left-right and updownv quadrants of the circle through which sajid `antenna structure passes and which utilizes the reecte'd pulses from an object to be detected, f'

an electronic indicating arrangement for -distinguishing between the reflected pulses received by said locating system during the lantennay rotation in said diierent quadrants; 4said arrange-7V me'nt comprising a pair of cathode ray tubes at said locating system, means for applying received pulses to one of said tubes during only the mo-v tion of said antenna structure through said leftright quadrant and to the other of saidrtubes .during only the motion of said antenna structure through said up-down quadrants, means for sweeping each of the cathode'rays of said tubes along a time axis` in synchronism with said pulse transmission, and means responsive to said antenna rotation for displacing the cathode ray sweep of said one tube during the antenna rotation through one of the left-right quadrants and for displacing the cathode ray sweep of the other tube during the antenna rotation through one of the up-down quadrants.

8. An obstacle detection system comprising a transmitter for periodically sending short wave carrier pulses of short duration spaced in time an amount which is large compared to the time of each pulse, a directive antenna system for said transmitter including a parabolic reector having a radiating element positioned oi-center, a two-pole synchronous motor for rotating said radiating element in a circular path, whereby the pattern of said antenna system periodically assumes a plurality of beam positions, an electronic tube indicating system, and electronic means coupled to said rotating radiating element for applying to said electronic tube system potentials during only such times when said radiating element is in certain positions.

9. A directive antenna having a synchronous driving motor for causing said antenna to .sequentially assume different positions of effectiveness, a transmitting system for applying pulses to said antenna to be radiated thereby during said different positions, a cathode ray circuit, an electronic means having an input circuit responsive to the motion of said driving motor solely during certain positions thereof and an output circuit coupled to said cathode ray circuit, whereby said cathode ray circuit indicates by characteristic markings the different beam ring positions of said antenna.

10. In an obstacle detection system employing an antenna which assumes a plurality of beam positions periodically, and a transmitter and a receiver coupled to said antenna, the method of operation which includes generating pulses which are short compared to the time interval between them, radiating a pulse from said anceiving on said antenna reected pulses returned from a remote obstacle upon which said radiated pulses impinge, producing electronic indications of said received reected pulses by means of a stream of charged particles. electronically producing a pulse during selected ones of said beam positions, and defiecting said stream of charged particles by said pulse only during said selected firing positions.

NILS E. LINDENBLAD.

REFERENCES CITED The following references are of record in th le of this patent:

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